Ink-jet recording sheet

ABSTRACT

An ink-jet recording sheet comprises a support, and provided thereon, an ink absorption layer containing solid fine particles, a hydrophilic binder, and oil drops in an amount of 5 to 50 weight % based on the solid fine particle weight, the content ratio by weight of the solid fine particles to the hydrophilic binder being 2 to 200, wherein the oil drops comprise an hydrophobic organic compound having a melting point of 40° C. or less or polymer particles having a glass transition temperature of 40° C. or less.

FIELD OF THE INVENTION

The present invention relates to a recording sheet for ink-jetrecording, and particularly to a recording sheet with improved inkabsorption property.

BACKGROUND OF THE INVENTION

Ink jet recording records an image or text on a recording sheet such asa paper sheet, applying various principles. This recording method hasadvantages in providing a relatively high speed recording, low noise andeasy color image formation. There have been problems in maintenance orink clogging of nozzles in this method, but improvements have been madein the ink and related device, and this method has been widely appliedto various fields such as printers, facsimile devices and computerterminals.

It is required for ink recording sheet to accept printing dots at highdensity and bright image tone, to provide rapid ink absorption propertyproducing no ink diffusion or blur in overlapped printed dots, and toprovide printing dots with smooth periphery and no blurring in whichprinting ink is not so greatly diffused.

In recording sheets slow in ink absorption, two or more kinds of colorink drops repel one another at overlapped ink recording portions on thesheet, resulting in image unevenness, or different color inks atdifferent but adjacent ink recording portions on the sheet are diffusedand mixed, resulting in deterioration of image quality. Therefore, arecording sheet having high ink absorption property is eagerly sought.

Many techniques have been proposed in order to solve the above describedproblems.

There have been proposed, for example, an ink jet recording sheet paperof low size content wetted with surface treatment coating disclosed inJapanese Patent O.P.I. Publication No. 52-53012, an ink jet recordingsheet paper comprising a support and provided thereon, an ink absorptionlayer disclosed in Japanese Patent O.P.I. Publication No. 55-5830, anink jet recording sheet paper comprising a layer containingnon-colloidal silica powder as pigment disclosed in Japanese PatentO.P.I. Publication No. 56-157, an ink jet recording sheet papercomprising an inorganic and organic pigment disclosed in Japanese PatentO.P.I. Publication No. 57-107878, an ink jet recording sheet papercomprising two void distribution peaks disclosed in Japanese PatentO.P.I. Publication No. 58-110287, an ink jet recording sheet papercomprising two upper and lower porous layers disclosed in JapanesePatent O.P.I. Publication No. 62-111782, an ink jet recording sheetpaper comprising amorphous cracks disclosed in Japanese Patent O.P.I.Publication Nos. 59-68292, 59-123696 and 60-18383, an ink jet recordingsheet paper comprising a fine powder layer disclosed in Japanese PatentO.P.I. Publication Nos. 61-135786, 61-148092 and 62-149475, an ink jetrecording sheet paper comprising pigments or fine particle silica eachhaving a specific physical property disclosed in Japanese Patent O.P.I.Publication Nos. 63-252779, 1-108083, 2-136279, 3-65376 and 3-27976, anink jet recording sheet paper comprising fine particle silica such ascolloidal silica disclosed in Japanese Patent O.P.I. Publication Nos.57-14091, 60-219083, 60-210984, 61-20797, 61-188183, 5-278324, 6-92011,6-183134, 7-137431 and 7-276789, or an ink jet recording sheet papercomprising hydrated alumina fine particles disclosed in Japanese PatentO.P.I. Publication Nos. 2-276671, 3-67684, 3-215082, 3-251488, 4-67986,4-263983 and 5-16517.

An ink receiving layer, if it is a layer (hereinafter referred to as avoid layer) having many voids to absorb or support ink, has good inkabsorption property and provides high image quality with no blurring.

The void volume occasionaly changes during storage under hightemperature and high humidity, and the void layer preferably containssolid fine particles to keep the void volume constant.

It is necessary that, in order to obtain a stable void layer containingsolid fine particles, a hydrophilic binder be incorporated in the voidlayer. However, if the addition amount of the hydrophilic binder is toolarge relative to that of the solid fine particles, it has problems inthat the hydrophilic binder fills spaces formed among the solid fineparticles or swells at initial ink absorption to fill voids in the voidlayer and results in deterioration of ink absorption. Accordingly, theaddition amount of the hydrophilic binder is limited.

The present inventors have made an extensive study and have found thatthe addition amount ratio by weight of the hydrophilic binder to thesolid fine particles is necessary to be about 2 to 200. However, a highaddition amount ratio of the solid fine particles brings about layerbrittleness, and fine cracks occur on the ink absorption layer surface,particularly during storage under low humidity. When ink jet recordingink is provided on the recording sheet having such high addition amountratio of the solid fine particles, the recording ink diffuses along thecracks occurred, resulting in serious deterioration of image quality.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above.

An object of the invention is to provide an ink jet recording sheet,comprising an ink absorption layer with high ink absorption propertycontaining solid fine particles dispersed in a hydrophilic binder, whichis capable of giving a high quality image without bringing about the inkabsorption layer brittleness, even after storage under low humiditycondition.

DETAILED DESCRIPTION OF THE INVENTION

The above objects of the invention can be attained by the followings:

1. an ink-jet recording sheet comprising a support, and providedthereon, an ink absorption layer containing solid fine particles, ahydrophilic binder, and oil drops in an amount of 5 to 50 weight % basedon the solid fine particle weight, the content ratio by weight of thesolid fine particles to the hydrophilic binder being 2 to 200, whereinthe oil drops comprise an hydrophobic organic compound having a meltingpoint of 40° C. or less or polymer particles having a glass transitiontemperature of 40° C. or less,

2. the ink-jet recording sheet of item 1 above, wherein the oil dropshave an average oil drop size of 0.05 to 0.5 μm,

3. the ink-jet recording sheet of item 1 above, wherein the solid fineparticles are selected from the group consisting of silica, calciumcarbonate, alumina, hydrated alumina and magnesium silicate, each havingan average primary order particle size of 7 to 80 nm,

4. the ink-jet recording sheet of item 1 above, wherein the solid fineparticles are manufactured by a gas phase reaction method,

5. the ink-jet recording sheet of item 1 above, wherein the hydrophilicbinder is polyvinyl alcohol or cation-modified polyvinyl alcohols, or

6. the ink-jet recording sheet of item 5 above, wherein the hydrophilicbinder has an average polymerization degree of 2,000 to 4,000.

The present invention will be detailed below.

The solid fine particles used in the invention include conventionalsolid fine particles usually used for ink recording sheet. The inorganicfine particles are preferable as fine particles, and include whiteinorganic pigment such as light calcium carbonate, heavy calciumcarbonate, magnesium carbonate, kaolin, clay, talc, calcium sulfate,barium sulfate, titan dioxide, zinc oxide, zinc hydroxide, zinc sulfide,zinc carbonate, hydrosulfite, aluminum silicate, diatomaceous earth,potassium silicate, magnesium silicate, synthetic non-crystallinesilica, colloidal silica, alumina, colloidal alumina, hydrated alumina,pseudo-boehmite, aluminum hydroxide, lithopone, zeolite, and magnesiumhydroxide. These inorganic fine particles may be used by being uniformlydispersed in a binder in primary order particle form or in aggregatedsecondary order particle form.

The organic fine particles include polystyrene, polymethacrylates,polyacrylamides, polyethylene, polypropylene, polyvinyl chloride,polyvinylidene chloride or coplymers thereof, or a urea resin or amelamine resin.

In the invention, inorganic solid fine particles are preferably used inobtaining a void layer having a relatively high void ratio. Silica,calcium carbonate, magnesium silicate, alumina or hydrated alumina amongthe inorganic solid fine particles, since high glossiness and highdensity image are easy to obtain.

Conventional various silica fine particles can be used as silica fineparticles preferably used in the ink jet recording sheet of theinvention.

The silica fine particles include synthetic silica synthesized by a wetmethod or a gas phase reaction, colloidal silica, porous silica in whichprimary particles aggregate to secondary particles and silica if anyshape. The examples thereof include synthetic amorphous silica disclosedin Japanese Patent O.P.I. Publication Nos. 55-51583 and 56-148583,silica super fine particles disclosed in Japanese Patent O.P.I.Publication No. 60-204390, fluorine-containing synthetic amorphoussilica disclosed in Japanese Patent O.P.I. Publication No. 60-222282,synthetic amorphous silica surface-treated with a silane coupling agentdisclosed in Japanese Patent O.P.I. Publication Nos. 60-224580 and62-178384, spherical silica disclosed in Japanese Patent O.P.I.Publication Nos. 62-183382 and 63-104878, synthetic silica fineparticles containing Na₂O in an amount of 0.5% by weight or moredisclosed in Japanese Patent O.P.I. Publication No. 63-317381, syntheticsilica fine particles having a specific surface area of 100 m²/gdisclosed in Japanese Patent O.P.I. Publication No. 1-115677, syntheticsilica fine particles surface-treated with alumina disclosed in JapanesePatent O.P.I. Publication No. 62-286787, synthetic silica fine particlessurface-treated with Ca, Mg or Ba disclosed in Japanese Patent O.P.I.Publication No. 1-259982, synthetic silica fine particles having an oilabsorption of 180 ml/g or more, colloidal silica disclosed in JapanesePatent O.P.I. Publication No. 57-14091, cationic colloidal silicadisclosed in Japanese Patent O.P.I. Publication Nos. 60-219084, 6-92011,6-297830 and 7-81214 and beaded or branched colloidal silica disclosedin Japanese Patent O.P.I. Publication No. 5-278324 and 7-81214.

Silica super fine particles with an average particle size of 7 to 80 nmis preferably used in order to obtain high glossiness or high voidamount. The silica super fine particles may be surface-modified with acation or surface-treated with Al, Ca, Mg or Ba. In the invention,silica synthesized by a gas phase reaction is most preferable.

Calcium carbonate preferably used in the ink jet recording sheet of theinvention includes light calcium carbonate having a predeterminedspecific surface area disclosed in Japanese Patent O.P.I. PublicationNos. 57-12486, 57-129778, 58-55283 and 61-20792, needle calciumcarbonate disclosed in Japanese Patent O.P.I. Publication Nos. 63-27277and 4-250091, calcium carbonate fine particles in which needle primaryparticles aggregate to needle secondary particles disclosed in JapanesePatent O.P.I. Publication No. 3-251487, needle rhombic algodonitecalcium carbonate having a specific oil absorption disclosed in JapanesePatent O.P.I. Publication Nos. 4-250091 and 4-260092, and sphericalsedimentating calcium carbonate disclosed in Japanese Patent O.P.I.Publication No. 7-40648.

The calcium carbonate has an average particle size of preferably 7 to 80nm, since it provides high glossiness or high void amount.

The magnesium silicate preferably used in the invention may beamorphous, spherical or tabular, but is preferably tabular. The averageparticle size of the tabular magnesium silicate is represented by adiameter of circle having an area corresponding to the average projectedarea of the tabular magnesium silicate, and is preferably 7 to 80 nm.

The alumina or hydrated alumina preferably used in the invention may becrystalline or non-crystalline, and may be amorphous, spherical orneedle particles or may be of any shape.

The average particle size of the above solid fine particles isrepresented by a diameter of a circle having an area corresponding tothe average projected area of particles photographed by an electronmicroscope.

The above solid fine particles preferably used in the invention isespecially preferably primary particles having an average particle sizeof 7 to 80 nm.

It is necessary in the ink jet recording sheet of the invention that ahydrophilic binder be contained in the solid fine particle-containinglayer in order to form a layer film.

The hydrophilic binder herein referred to is a polymer having asolubility at room temperature in water of 0.1 weight % or more.

The hydrophilic binder used in the ink jet recording sheet of theinvention includes gelatin or its derivative, polyvinyl pyrrolidone(having an average molecular weight of preferably about 200,000 ormore), pullulan, polyvinyl alcohol or its derivative (having an averagemolecular weight of preferably about 20,000 or more), polyethyleneglycol (having an average molecular weight of about 100,000 or more),carboxymethyl cellulose, hydroxyethyl cellulose, dextrane, dextrin,polyacrylic acid or its salt, agar, κ-carrageenin, λ-carrageenin,τ-carrageenin, xanthan gum, locust bean gum, alginic acid, gum arabic,polyalkyleneoxide copolymers disclosed in Japanese Patent O.P.I.Publication Nos. 7-195826 and 7-9757, a water-soluble polyvinyl butyral,and a homopolymer or copolymer obtained by polymerizing a vinyl monomerhaving a carboxy group or a sulfonic acid group disclosed I JapanesePatent O.P.I. Publication No. 62-245260. These hydrophilic binders maybe used singly or in combination.

It is preferable in less moisture absorption, less tackiness and lessblurring after ink jet recording that the ink absorption layer containat least polyvinyl alcohol or cation-modified polyvinyl alcohol.

The polyvinyl alcohol has an average polymerization degree of preferably500-4,000, and more preferably 2,000-4,000 in minimizing crackoccurrence. The polyvinyl alcohol has a saponification degree ofpreferably 70 to 100%, and more preferably 80 to 99%.

The cation-modified polyvinyl alcohol is obtained by saponificated acopolymer of vinyl actate and an ethylenically unsaturated monomerhaving a cationic group.

The ethylenically unsaturated monomer having a cationic group includestri-methyl-(2-acrylamide-2,2-dimethylethyl) ammonim chloride,tri-methyl-(3-acrylamide-3,3-dimethylpropyl)ammonim chloride,N-vinylimidazole, N-vinyl-2-methylimidazole,N-(3-dimethylaminopropyl)methacrylamide,tri-methyl-(3-methacrylamidopropyl)ammonim chloride, andN-(1,1-dimethyl-3-dimethylaminopropyl) acrylamide.

The content of the monomer having a cationic group in thecation-modified polyvinyl alcohol is preferably 0.1 to 10 mol %, morepreferably 0.2 to 5 mol%, based on the vinyl acetate content. Thecation-modified polyvinyl alcohol has an average polymerization degreeof ordinarily 500 to 4,000, preferably 2,000 to 4,000. Thesaponification degree of the vinyl acetate group is ordinarily 60 to100%, and preferably 70 to 99%.

The layer containing solid fine particles in the invention contains theabove polyvinyl alcohol or cation-modified polyvinyl alcohol in anamount of preferably 60% or more by weight, more preferably 80 to 100%by weight based on the total hydrophilic binder weight.

In the ink jet recording sheet of the invention, the weight ratio of thesolid fine particles to the hydrophilic binder is 2 to 200 in the inkabsorption layer. The low void ratio as in the ratio less than 2requires a large layer thickness to completely absorb ink, the largethickness resulting in various problems, or the low void ratio swellsthe layer by ink absorption of the binder and lowers ink absorptionspeed of the layer. On the other hand, the ratio exceeding 200 bringsabout layer brittleness even by employing various counter measuresdescribed later, resulting in poor image quality. The ratio ispreferably 2.5 to 100, and especially preferably 3 to 50. When thesilica synthesized by a gas phase reaction is used as solid fineparticles, the ratio is especially preferably 3 to 20.

The ink absorption layer of the ink jet recording sheet of the inventionhas a high solid fine particle content to the hydrophilic binder, and inorder to improve the layer brittleness caused by the high solid fineparticle content, it is necessary that the ink absorption layer containoil drops in an amount of 5 to 50 weight % based on the solid fineparticle weight.

The oil drops herein referred to include two kinds of groups, the firstone is oil drops comprising a hydrophobic organic compound with amelting point of 40° C. or less, preferably −40 to 40° C. and the secondone is oil drops comprising polymer particles having a glass transitiontemperature of 40° C. or less, preferably −40 to 40° C. The polymerparticles are preferably obtained from those dispersed in a polymerlatex. The hydrophobic organic compound is an organic compound having asolubility in water at room temperature of 0.1 weight % or less,preferably 0.01 weight % or less.

The hydrophobic organic compound includes a conventional hydrophobichigh boiling point organic solvent and a hydrophobic polymer with amelting point of 40° C. or less. The hydrophobic compound includesphthalates (for example, dibutylphthalate, dioctylphthalate,diisodecylphthalate), phosphates (for example, tricresylphosphate,trioctylphosphate), fatty acid esters (for example, butyl stearate,bis(2-ethylhexyl) sebatate, ethylene glycol distearate, glyceroltributylate), amides (for example, N,N-diethyllaurylamide,N,N-diethyl-2-(2,5-di-t-amylphenoxy)butanamide), ethers (for example,ethylene glycol dibutylether, decylether, dibenzylether), silicone oiland liquid paraffin.

The hydrophobic polymer includes poly(2-ethylhexyl methacrylate),polybutyl methacrylate, coploy(butylacrylate/hydroxyethyl methacrylate,90/10), polyvinyl acetate, polyvinyl propionate,coploy(butylacrylate/t-butylacrylate/2-ethylhexyl methacrylate/styrene,60/20/10/10). The hydrophobic polymer has an average molecular weight ofpreferably 5,000 to 100,000. The hydrophobic polymer having an averagemolecular weight exceeding 100,000 is difficult to form fine oil dropsby an emulsifying method described later.

The hydrophobic organic compound is emulsified in a hydrophilic binderpreferably in a surfactant employing a high speed homoginizer or a ahigh pressure homogenizer. It is preferable in forming fine oil dropsthat the emulsification is carried out in the presence of a low boilingpoint organic solvent such as ethyl acetate, propyl acetate, methylethylketone, acetone, or N,N-dimethylformamide. On emulsification, anotherhydrophobic organic compound (such as a UV absorbent, a brighteningagent or an image stabilizing agent) exceeding a melting point of 40° C.can be used in combination, but preferably, oil drops contain 50 or moreweight % of a compound with a melting point of 40° C. or less.

The second one, the polymer latex containing polymer particles having aglass transition temperature of 40° C. or less is a polymer latexobtained by an emulsion polymerization method, for example, astyrene-butadiene coploymer latex, polyacrylate latex, apolymethacrylate latex, a polyvinyl acetate latex, or an ethylene-vinylacetate coploymer latex. The example thereof includes styrene-butadiene(7/3) latex, polyvinyl acetate latex, vinyl acetate-ethylene (9/1)latex, vinyl acetate-ethylmethacrylate (5/5) latex, vinylchloride-ethylacrylate (3/2) latex, ethylacrylate-methylacrylate-HEMA(5/4/1) latex, styrene-butylacrylate-HEMA (1/6/3) latex, and siliconelatex. In the above, the number in the parenthesis represents acopolymerization mol ratio, and HEMA representshydroxyethylmethacrylate.

The average oil drop size of the oil drops is preferably 0.05 to 0.5 μm.The oil drop content of the ink absorption layer is 5 to 50 weight %,preferably 10 to 40 weight %, based on the solid fine particle weightcontent. When the oil drop content is less than 5 weight %, brittlenessof the absorption layer is not sufficiently improved. In contrast, whenthe oil drop content exceeds 50 weight %, the void ratio of theabsorption layer is lowered, and ink absorption and glossiness of theabsorption layeris is likely to be deteriorated.

The solid fine particle content of the ink absorption layer ispreferably 7 to 35 g/m², and more preferably 10 to 30 g/m².

The ink-jet recording sheet of the invention may comprise two or moreink absorption layers containing a hydrophilic binder and solid fineparticles. In the above plural layers, kinds of the hydrophilic binderand solid fine particles or the content ratio of the hydrophilic binderand solid fine particles may be suitably selected, but at least one inkabsorption layer has a content ratio by weight of the solid fineparticles to the hydrophilic binder of 2 to 200 and contains the oildrops. The thickness of the ink absorption layer is preferably 10 to 60μm, and more preferably 20 to 50 μm.

The ink-jet recording sheet of the invention has an ink absorption layercontaining the above described solid fine particles and hydrophilicbinder, and may further have another hydrophilic layer. Such anotherhydrophilic layer is preferably provided farther from the support thanthe ink absorption layer on the ink absorption layer side. Thehydrophilic layer has a dry thickness of 2 μm or less and preferably 1.5μm or less, in view of ink absorption speed.

Any layer on the ink absorption layer side of the support in the ink-jetrecording sheet of the invention optionally contains various additives.

The additives include a UV absorbent disclosed in Japanese Patent O.P.I.Publication Nos. 57-74193, 57-87988 and 62-261476, an anti-fading agentdisclosed in Japanese Patent O.P.I. Publication Nos. 57-74193, 57-87988,60-72785, 61-146591, 1-95091 and 3-13376, an anionic, cationic ornonionic surfactant, and a fluorescent brightening agent, a pH adhustingagent such as sulfuric acid, phosphoric acid, citric acid, sodiumhydroxide, potassium hydroxide or potassium carbonate, an anti-formingagent, a wetting agent such as ethylene glycol, an anti-septic agent, athickner, a haredener, an anti-static agent and a matting agentdisclosed in Japanese Patent O.P.I. Publication Nos. 59-42993, 59-52689,62-280069, 61-24287 and 4-219266.

The hardener includes an inorganic or organic hardener such as chromalum, formaldehyde, glyoxal, an epoxy compound, a vinyl sulfonecompound, an acroyl compound, a s-triazine compound, an N-methylolcompound, a carbodiimide compound or an ethyleneimine compound.

The solid coating amount of a layer on the ink recording surface side ofthe support in the ink jet recording sheet of the invention is notspecifically limited, but is preferably about 10 to 40 g/m², and more ispreferably about 20 to 30 g/m². The layer is preferably thinner in viewof minimizing curling of the recording sheet after recording.

The layer on the ink recording surface side of the support in the inkjet recording sheet of the invention may contain, as a water resistantagent, a polycationic electrolyte disclosed in Japanese Patent O.P.I.Publication No. 56-84992, a polyarylamine disclosed in Japanese PatentPublication No. 4-15744 and Japanese Patent O.P.I. Publication Nos.61-58788 and 62-174184 or an alkali metal salt of a weak acid disclosedin Japanese Patent O.P.I. Publication No. 61-47290.

The support used in the ink jet recording sheet of the inventionincludes well-known, conventional supports for a ink jet recordingsheet.

The transparent support in the invention includes a resin film or platesuch as a polyester resin, a polyester resin, a diacetate resin, atriacetate resin, an acryl resin, a polycarbonate resin, a polyvinylchloride resin, a polyimide resin, cellophane or celluloid and a glassplate. The support is preferably a heat resistant film, when used for anover-head projector, and especially preferably a polyethyleneterephthalate film. The thickness of the transparent support ispreferably about 10 to 200 μm.

The translucent support includes a sheet or plate such as paper,resin-coat paper, cloth, wood or metal and a support in which the abovetransparent support is made translucent by a well-known method. Thetranslucent support is preferably a resin-coat paper (so-called RCpaper) in which a polyolefin resin containing white pigment is providedat least one surface of a base paper sheet or a polyethyleneterephthalate sheet (so-called white PET) containing white pigment.

The present invention is markedly effected especially by awater-repellent support, and the especially preferable is a plasticsupport such as a transparent or translucent polyethylene terephthalateor a support in which a hydrophobic resin such as a polyethylene resinis coated on both surfaces of a base paper sheet.

In order to increase adhesion between a support and an ink receivinglayer comprising the ink absorption layer, the support is preferablysubjected to corona discharge treatment or subbing treatment before theink receiving layer coating. The ink jet recording sheet of theinvention need not be colorless, and may be colored.

In the manufacture the ink jet recording sheet of the invention, amethod of coating the ink receiving layer on a support can be selectedfrom the conventional ones.

The coating method includes a roller coating method, a rod-bar coatingmethod, an air-knife coating method, a spray coating method, a curtaincoating method and an extrusion coating method using a hopper disclosedin U.S. Pat. No. 2,681,294.

The water based ink herein referred to is a recording liquid comprisingthe following colorants, solvents and other additives. The colorantincludes a direct dye, an acid dye, a basic die, a reactive dye and fooddyes, each being well known in the art.

The solvent for water based ink includes water and a water solubleorganic solvent, for example, alcohols such as methyl alcohol, isopropylalcohol, n-butyl alcohol, tert-butyl alcohol and iso-butyl alcohol,amides such as dimethylformamide and dimethylacetoamide, ketones orketonealcohols such as acetone and diacetone alcohol, ethers such astetrahydrofurane and dioxane, polyalkylene glycols such as polyethyleneglycol and polypropylene glycol, polyhydric alcohols such as ethyleneglycol, propylene glycol, butylene glycol, triethylene glycol,1,3,6-hexane triol, thiodiglycol, hexylene glycol, diethylene glycol,glycerin and triethanol amine and polyhydric alcohol lower alkyl etherssuch as ethylene glycol methylether, diethylene glycol methyl(orethyl)ether and triethylene glycol monobutylether. Of these, polyhydricalcohols such as diethylene glycol, glycerin and triethanol amine orpolyhydric alcohol lower alkyl ethers such as triethylene glycolmonobutylether is preferable.

The other additives include a pH adjusting agent, a metal chelatingagent, an anti-fungal, a viscosity adjusting agent, a surface tensionadjusting agent, a wetting agent, a surfactant and an anti-rust agent.

The water based ink has a surface tension at 20° C. of preferably 25 to60 dyne/cm, and more preferably 30 to 50 dyne/cm.

EXAMPLES

The invention will be detailed in the following examples, but theinvention is not limited thereto. In the examples, “%” represents weight%, unless otherwise specified. The addition amount represents amount perm² of ink jet recording sheet.

Example 1

The following Coating Solution-1 was coated on a photographic printpaper to give a wet thickness of 190 μm, and dried to obtain an inkabsorption layer having a dry thickness of 25 μm. Thus, Ink jetrecording sheet sample No. 1 was obtained. The paper was one in which apolyethylene film was laminated on both surfaces of a 160 g/m² basepaper, the polyethylene film on an ink recording layer side containinganatase type titanium dioxide in an amount of 12 weight %. The coatingwas carried out using a slide hopper coating method, and after thecoating, the coated layer was cooled to about 10° C., dried by applyinga 10° C. air for 1 minute, and further dried by applying a 30-45° C. airfor 4 minutes.

(Coating Solution-1) Pure water (Ion-exhange water) 980 ml Ethanol 50 mlSilica (silica by a gas phase reaction 51 g having an average primaryparticle size of about 13 nm) Polyvinyl alcohol (an average 8 gpolymerization degree of 3,500, saponification degree of 88%)Surfactant-1 (AS-1) 0.1 g AS-1

Ink jet recording sheet sample Nos. 2 through 11 were prepared in thesame manner as in Ink jet recording sheet sample No. 1, except thatadditives as shown in Table 1 was further added to Coating Solution 1.Each additive was added in the form of an emulsion in which the additivewas emulsified in the polyvinyl alcohol in the presence of AS-1. Thetotal amount of the coating solutions was adjusted with pure water tokeep constant.

TABLE 1 Average Oil *Addition Recording Sheet Drop Size Amount SampleNo. Additives (mp) (μm) (wt %)  2 (Comparative) Liquid paraffin 0.3   3(mp <10° C.)  3 (Invention) Liquid paraffin 0.3  10 (mp <10° C.)  4(Invention) Liquid paraffin 0.3  20 (mp <10° C.)  5 (Comparative) Liquidparaffin 0.3  90 (mp <10° C.)  6 (Comparative) DIDP (mp = 53° C.) 0.32 3  7 (Invention) DIDP (mp = 53° C.) 0.32 10  8 (Invention) DIDP (mp =53° C.) 0.32 20  9 (Comparative) DIDP (mp = 53° C.) 0.32 90 10(Comparative) Solid paraffin 0.36 20 (mp = 60° C.) 11 (Comparative) DPP(mp = 74° C.) 0.28 20 DIDP: Diisodecylphthalate DPP: Diphenylphthalate*In Table 1, the addition amount represents the additive weight contentbased on the silica weight.

An evaluation image pattern was printed on each of the above obtainedink jet recording sheet samples using an ink-jet printer MJ-900Cproduced by Epson Co., Ltd., and evaluated regarding the followingitems.

(1) Ink Absorption

Yellow and cyan ink were uniformly jetted in 40% of maximum ink jettingamount, respectively, on each of the ink jet recording sheet samples toform a mixture color solid image. The red reflection densities of twentypoints of the resulting solid image were measured by a microdensitometer(aperture=200 μmφ. The standard deviation of the resulting densities wasdivided by the average density to obtain a variation coefficient. Whenink absorption is good and results in an image without unevenness, thiscoefficient is small, however, when poor ink absorption causes beadingamong the jetted ink drops and results in an image with unevenness, thiscoefficient is large.

(2) Layer Brittleness

Each of the samples obtained above was stored at 25° C. and at 20% RHfor 24 hours in 60 mm cylindrical form with the recording layer outward,and thereafter, the recording layer surface was observed with amagnifying glass according to the following criteria:

A: No cracks observed

B: Some cracks observed, but no practical problem in image quality

C: Cracks observed, and problem in image quality, but no cracks observedun-aided visually

D: Cracks observed un-aided visually, and serious problem in imagequality

(3) Glossiness

Glossiness of the ink absorption layer was measured at an angle of 75°by a glossmeter VGS-1001-DP produced by Nihon Denshoku Kogyo Co., Ltd.

The results are shown in Table 2.

TABLE 2 Recording Sheet Ink Sample No. Absorption Cracks Glossiness  1(Comparative) 0.04 D 61%  2 (Comparative) 0.04 D 61%  3 (Invention) 0.05B 60%  4 (Invention) 0.06 B 58%  5 (Comparative) 0.10 B 38%  6(Comparative) 0.04 D 60%  7 (Invention) 0.05 B 61%  8 (Invention) 0.06 B59%  9 (Comparative) 0.11 B 43% 10 (Comparative) 0.05 D 46% 11(Comparative) 0.06 D 53%

As is apparent from Table 2, Recording Sheet Sample Nos. 3, 4, 7, and 8greatly improved the layer strength without lowering of ink absorptionand glossiness. In contrast, Recording Sheet Sample Nos. 2 and 6, whichcontain oil drops in the mount less than in the invention, exhibited noimproved layer strength, and Recording Sheet Sample Nos. 5 and 9, whichcontain oil drops in the amount more than in the invention, exhibitedlowering of ink absorption and glossiness. Further, Samples employingadditives having a melting point exceeding 40° C. exhibited no improvedlayer strength.

Example 2

Ink jet recording sheet sample Nos. 21 through 28 were prepared in thesame manner as in Ink jet recording sheet sample No. 1, except that thepolymer latexes as shown in Table 3 was further added to CoatingSolution 1. The resulting samples were evaluated in the same manner asin Example 1. The results are shown in Table 4.

TABLE 3 Average Oil *Addition Recording Sheet Additives Drop Size AmountSample No. (mp or Tg) (μm) (wt %) 21 (Invention) ET/VA (Tg <20° C.) 0.1010 22 (Invention) ET/VA (Tg <20° C.) 0.10 30 23 (Comparative) ET/VA (Tg<20° C.) 0.10 60 24 (Invention) ST/BA/HEMA 0.09 10 (Tg <20° C.) 25(Invention) ST/BA/HEMA 0.09 30 (Tg <20° C.) 26 (Comparative) ST/BA/HEMA0.09 60 (Tg <20° C.) 27 (Comparative) ST (Tg: about 100° C.) 0.12 20 28(Comparative) BMA (Tg: about 57° C.) 0.08 20 ET/VA: Ethylene/ethylacetate (10/90) copolymer latex ST/BA/HEMA:Styrene/butylacrylate/hydroxyethylmethacrylate (20/70/10) copolymerlatex ST: Polystyrene latex BMA: Poly butylmethacrylate latex *In Table3, the addition amount represents the additive weight content based onthe silica weight.

TABLE 4 Recording Sheet Ink Sample No. Absorption Cracks Glossiness 21(Invention) 0.05 B 62% 22 (Invention) 0.07 B 64% 23 (Comparative) 0.13 A48% 24 (Invention) 0.05 B 59% 25 (Invention) 0.06 B 57% 26 (Comparative)0.11 B 45% 27 (Comparative) 0.07 D 51% 28 (Comparative) 0.08 C 42%

As is apparent from Table 4, Recording Sheet Sample Nos. 21, 22, 24 and25, which employed the polymer latex with a glass transition temperaturenot more than 40° C. in the amount of 5 to 50 weight % based on thesilica weight, greatly improved the layer strength without lowering inkabsorption and glossiness. In contrast, Recording Sheet Sample Nos. 23,and 26, which employed the polymer latex in the amount exceeding 50weight % based on the silica weight, improved the layer strength butexhibited lowering of ink absorption and glossiness. Further, samplesemploying a polymer latex having a glass transition temperatureexceeding 40° C. exhibited no improved layer strength.

Example 3

The following Coating Solution-2 was coated on a paper support, in whicha polyethylene film was laminated on both surfaces of a 100 g/m² basepaper, to give a wet thickness of 150 μm, dried, and then, CoatingSolution-3 was further coated on the above coated layer and dried toobtain an ink absorption layer. The paper support was a support having athickness of 140 μm in which a polyethylene film containing an anatasetype titanium dioxide in an amount of 7 weight % was laminated on thesurface of the base paper on the ink recording layer side, and a layercontaining an alkali-processed gelatin in an amount of 4.2 g/m² and ahardener was provided on the surface of the support opposite the inkrecording layer.

(Coating Solution-2) Pure water 980 ml Fine particle silica having anaverage 48.0 g particle size of about 0.007 μm Polyvinyl alcohol (PVA3500) of an average 10.8 g polymerization degree of 3,500(saponification degree of 94%) Surfactant-1 (AS-1) 1.2 g

Thereafter, the following Coating Solution-3 was coated on the inkabsorption layer to give a wet thickness of 8 μm, and dried. Thus, InkJet Recording Sheet 31 was obtained.

(Coating Solution-3) Pure water 800 ml Phenylcarbamoylated gelatin 40 g(carbamoylation degree of about 88%) Polyvinyl pyrrolidone (K-90) 25 gPolyethylene oxide (average molecular 12 g weight: about 150,000)Surfactant-2 (AS-5) 0.7 g Hardener-1 2.1 g AS-5

Hardener-1

Ink jet recording sheet sample Nos. 32 through 35 were prepared in thesame manner as in Ink Jet Recording Sheet Sample No. 31, except thatdispersions as shown in Table 5 was further added to Coating Solution 2.

Each dispersion was added in the form of aqueous solution or dispersion,but the pure water amount was added to keep the total amount of thecoating solutions constant.

TABLE 5 Recording Sheet *Amount of Oil Sample No. Dispersion Drops (wt%) 31 (Comparative) None  0 32 (Invention) LP Dispersion  60 ml  10 33(Invention) LP Dispersion 250 ml  42 34 (Comparative) LP Dispersion 600ml 100 LP Dispersion: 8% liquid paraffin dispersion *Amount of Oil Dropsrepresents the oil drop content based on the silica weight content.

The resulting samples were evaluated in the same manner as in Example 1.The results are shown in Table6.

TABLE 6 Recording Sheet Ink Sample No. Absorption Cracks Glossiness 31(Comparative) 0.10 D 74% 32 (Invention) 0.12 C 72% 33 (Invention) 0.13 B68% 34 (Comparative) 0.19 B 48%

As is apparent from Table 6, recording sheet samples having, as anoutermost layer, a swelling layer containing gelatin as a main componentlowers ink absorption but improves glossiness. Among these, RecordingSheet Samples Nos. 32 and 33 greatly improved the layer strength withoutlowering ink absorption and glossiness. In contrast, Recording SheetSample No. 34, which employed liquid paraffin in the amount of 100weight % based on the silica weight, improved the layer strength butexhibited greatly lowered ink absorption and glossiness.

Example 4

Ink jet recording sheet sample Nos. 41 was prepared in the same manneras in Ink Jet Recording Sheet Sample No. 31 of Example 3, except thatthe following Coating Solution 2a was used instead of Coating Solution2.

Ink jet recording sheet sample Nos. 42 through 44 were prepared in thesame manner as in Ink Jet Recording Sheet Sample No. 41 above, exceptthat the dispersions as shown in Table 7 were further added to theCoating Solution 2a.

(Coating Solution 2a) Pure water 920 ml Fine particle calcium carbonatehaving 120.0 g an average particle size of about 0.03 μm Polyvinylalcohol (PVA 1700) of an average 6.2 g polymerization degree of 1700(saponification degree of 90%) Surfactant-1 1.0 g

TABLE 7 Recording Sheet *Amount of Oil Sample No. Dispersions Drops (wt%) 41 None — 42 DIDP Dispersion  60 ml  5 43 DIDP Dispersion 250 ml 2144 DIDP Dispersion 600 ml 54 DIDP Dispersion: 10 wt %diisodecylphthalate disperion *In Table 7, the amount represents the oildrop content based on the silica weight.

The resulting samples were evaluated in the same manner as in Example 3.The results are shown in Table 8.

TABLE 8 Recording Sheet Ink Sample No. Absorption Cracks Glossiness 41(Comparative) 0.14 D 75% 42 (Invention) 0.14 C 74% 43 (Invention) 0.15 B70% 44 (Comparative) 0.23 B 53%

As is apparent from Table 8, recording Sheet Samples employing fineparticle calcium carbonate as solid fine particles exhibited the sameresults as Example 3.

Example 5

Ink jet recording sheet samples were prepared in the same manner as inExample 4, except that fine particle calcium carbonate of CoatingSolution 3 was replaced with fine particle magnesium silicate (averageparticle size 30 nm, thickness about 1 nm), and evaluated in the samemanner as in Example 4. The same results as Example 4 were obtained.

What is claimed is:
 1. An ink-jet recording sheet comprising a support,and provided thereon, an ink absorption layer containing, in admixture,solid fine particles, a hydrophilic binder having an averagepolymerization degree of 2,000 to 4,000, and oil drops in an amount of 5to 50 weight % based on the solid fine particle weight, the contentratio by weight of the solid fine particles to the hydrophilic binderbeing 2 to 200, wherein the hydrophilic binder is polyvinyl alcohol orcation-modified polyvinyl alcohols, and the oil drops comprise ahydrophobic organic compound having a melting point of 40° C. or lessand a solubility in water at room temperature of 0.1 weight % or less orpolymer particles having a glass transition temperature of 40° C. orless, said polymer particles being obtained from a polymer latexselected from the group consisting of a styrene-butadiene copolymerlatex, a polyacrylate latex, a polymethacrylate latex, a polyvinylacetate latex, and an ethylene-vinyl acetate copolymer latex.
 2. Theink-jet recording sheet of claim 1, wherein the oil drops have anaverage oil drop size of 0.05 to 0.5 μm.
 3. The ink-jet recording sheetof claim 2, wherein the solid fine particles are selected from the groupconsisting of silica, calcium carbonate, alumina, hydrated alumina andmagnesium silicate, each having an average primary order particle sizeof 7 to 80 nm.
 4. The ink-jet recording sheet of claim 1, wherein thesolid fine particles are selected from the group consisting of silica,calcium carbonate, alumina, hydrated alumina and magnesium silicate,each having an average primary order particle size of 7 to 80 nm.
 5. Theink-jet recording sheet of claim 1, wherein the solid fine particles aremanufactured by a gas phase reaction method.
 6. The ink-jet recordingsheet of claim 1, wherein the hydrophilic binder is polyvinyl alcohol.7. The ink-jet recording sheet of claim 1 wherein the oil drops comprisesaid polymer particles.
 8. The ink-jet recording sheet of claim 7,wherein the oil drops have an average oil drop size of 0.05 to 0.5 μm.9. The ink-jet recording sheet of claim 1, wherein said oil dropscomprise said hydrophobic organic compound.
 10. The ink-jet recordingsheet of claim 1, wherein the hydrophilic binder is cation modifiedpolyvinyl alcohol.
 11. The ink-jet recording sheet of claim 1, whereinthe support is a water-repellent support.
 12. The ink-jet recordingsheet of claim 11, wherein the ink absorption layer has a thickness of10 to 60 μm.
 13. The ink-jet recording sheet of claim 1, wherein the inkabsorption layer has a thickness of 10 to 60 μm.